Field of the Invention
The present invention relates to a high-side gate drive circuit.
Description of the Background Art
A high voltage metal oxide semiconductor (MOS) gate driver IC (HVIC) is a high-withstand voltage IC that directly drives a gate with an input signal, such as a microprocessor. The HVIC includes a high-side gate drive circuit that drives a high-voltage side (high-side) switching element and a low-side gate drive circuit that drives a low-voltage side (low-side) switching element.
The high-side gate drive circuit generates an on-pulse synchronized with the rising of a high-side input signal HIN and an off-pulse synchronized with the falling of the high-side input signal HIN. Levels of reference voltages for the on-pulse and the off-pulse are shifted from GND to a high voltage by high-withstand voltage level shift MOSFETs. The on-pulse and the off-pulse are then transmitted to a latch circuit in a high-voltage side logic circuit, and are output from an output circuit to the high-side switching element. In this way, a pulse width of a gate drive signal for the high-side switching element is determined.
Conventional high-side gate drive circuits have a problem that when a high-side switching element turns on or off, a voltage change dV/dt between a high-side floating power supply offset voltage VS and the ground GND becomes noise, preventing normal signal transmission to a high-voltage side.
A method of avoiding influence of noise by making periods of the on-pulse and the off-pulse longer than a noise period has been conventionally proposed for this problem. Japanese Patent Application Laid-Open No. 2003-79131 proposes a method of avoiding influence of noise, by the on-pulse and the off-pulse each including a plurality of pulses having a predetermined period.
However, there is a problem that the on-pulse and the off-pulse having a period longer than the noise period will lead to increase in a loss made when a signal is transmitted to the high-side switching element. Also, when the on-pulse and the off-pulse each include a plurality of pulses, it is necessary to set the pulse period constant in advance, although the noise period varies depending on an operating environment of the high-side switching element. Therefore, in a case where the high-side input signal is a narrow-width pulse, signal transmission from the high-side input signal to the high-side switching element will be delayed excessively. Therefore, there is a problem that input of the narrow-width pulse is limited or dead time increases.